1. Field of the Invention
The present invention relates to a multi-domain vertical alignment LCD (MVA-LCD) device and, more particularly, to an MVA-LCD device with color filters on a TFT array substrate for improving transmittance.
2. Description of the Related Art
To obtain a super-high image quality in LCDs for large-screen display products, multi-domain vertical alignment (MVA) mode LCD that provides high contrast ratio, rapid response time and wide view angle has been developed. Since using conventional rubbing method is difficult in controlling liquid crystal (LC) domains in MVA-LCD device, protrusions designed on the TFT array substrate and the color filter substrate, are employed to control the LC alignment automatically. This alignment technique is named ADF (automatic domain formation). The slopes of the protrusions can create either two or four kinds of domains to ensure ease in mass production.
FIG. 1A is a top view showing an MVA-LCD device according to the prior art. FIG. 1B is a sectional diagram along line I—I shown in FIG. 1A. The conventional MVA-LCD device 10 has a TFT array substrate 12I, a color filter substrate 12II, and a liquid crystal (LC) layer 14 formed in the space between the two parallel substrates 12I and 12II. On the TFT array substrate 12I, a plurality of transverse-extending scanning electrodes 16 and a plurality of lengthwise-extending signal electrodes 18 define square-shaped pixel areas arranging in a matrix form. Each of the pixel areas in covered by a pixel electrode 20, and has a TFT structure 19 near the intersection of the scanning electrode 16 and the signal electrode 18. Also, a plurality of lengthwise-extending first protrusions 22I is patterned on the pixel electrode 20, and covered by a first alignment layer 24I. Each of the first protrusions 22I is formed on the center region of each pixel area.
On the color filter substrate 12II, a plurality of black matrix layers 26 and a color resin layer 28 are stacked, and a plurality of transverse-extending common electrode 29 is formed on the color resin layer 28 to pass through pixel areas. Also, a plurality of lengthwise-extending second protrusions 22II are patterned on the common electrode 29, and covered by a second alignment layer 24II that faces the LC layer 14. Two of the second protrusions 22II are formed on the two sides of each pixel area.
The profile of the protrusions 22I and 22II can contribute to a multi-domain cell through a combination of pre-tilt control and a fringe electric field. Preferably, the first protrusion 22I is formed as a triangle profile, and the second protrusion 22II is formed as a reversed-triangle profile. For the LC molecules near the sidewalls of the protrusions 22I and 22II, the slope of the protrusions 22I and 22II causes the LC molecules tilt in a desired direction either when a voltage is applied across the pixel area or not. For the LC molecules away from the sidewalls of the protrusions 22I and 22II, the slope of the protrusions 22I and 22II and the lateral electric field cause the LC molecules tilt in a desired direction when a voltage is applied across the pixel area.
However, the first protrusions 22I on the TFT array substrate 12I and the second protrusions 22II on the color filter substrate 12II result in a low transmittance in the MVA-LCD device 10. Also, these protrusions 22I and 22II encounter a problem of high product costs.